Medial degeneration does not involve uniformly the whole ascending aorta: morphological, biochemical and clinical correlations.

Abstract

To investigate whether and how the severity of medial degeneration (MD) lesions varies along the circumference of the dilated intrapericardial aorta. Two groups of aortic wall specimens, respectively harvested 1cm distal to the non-coronary (NC) sinus (right postero-lateral wall) and to the right coronary sinus (anterior wall) in 22 patients undergoing surgery for dilatation of the intrapericardial aorta associated with aortic valve disease, were separately sent for pathology, morphometry and ultrastructural examination. MD lesions found at histology were classified into three degrees of severity. MD mean degree and morphometric findings in postero-lateral ('NC') and anterior ('coronary') specimens were compared by paired t-test. Correlation between degree of aortic dilatation at echocardiography and severity of MD was assessed separately for each of the two groups of specimens. After the preliminary results of the morphological study, we decided to send the specimens for biochemical investigation of protein electrophoretic patterns. This was performed in the last seven patients of this series. At histology, MD was found in all cases. A higher mean MD degree was found in the NC group (2.59+/-0.50 versus 1.59+/-0.67 in the coronary group; P<0.001). At morphometry, normal smooth muscle cells in the NC specimens were significantly reduced (P=0.012) and the length (P=0.011) and number (P=0.015) of elastic fibres reduced and increased, respectively. Correlation between aortic ratio and MD degree was significant in the NC specimens (P<0.001), not in the coronary ones (P=0.227). Quantitative differences between coronary and NC proteins from the same patient and between coronary proteins from different patients were found at electrophoresis. However, at this stage of the study, the sample was too small to allow for the identification of proteins involved in those differences. MD lesions in dilated intrapericardial aorta are more severe in the right postero-lateral wall area, likely due to haemodynamic stress asymmetry.